Heat exchanger

ABSTRACT

The invention relates to a heat exchanger ( 10 ) with tubes ( 80 ) and a collector box ( 20 ). Said collector box ( 20 ) has a tube-plate ( 30 ) with tube openings ( 60 ) and with angled or rounded lateral regions ( 110,120 ).

The present invention relates to a heat exchanger, in particular acharge-air cooler for a motor vehicle.

To increase the power of an internal combustion engine, it is possiblefor the air which is to be fed for combustion to be compressed, forexample using a turbocharger, before it is fed to the combustionchambers of the internal combustion engine. However, compressing the airat the same time also heats it, and this is disadvantageous for anoptimum sequence of the combustion process. By way of example, this cancause premature ignition or increased emissions of nitrogen oxides. Toavoid the disadvantageous consequences of combustion of superheated airsupplied, a heat exchanger designed as a charge-air cooler, which can beused to cool the compressed air to an acceptable temperature before itscombustion, is connected downstream of a turbocharger.

A charge-air cooler is described, for example, in DE 197 57 034 A1. Inthe heat exchanger disclosed therein, the hot air is introduced into afirst header passage of the heat exchanger, where it is distributed andflows into flat tubes which open out into the header passage. The flattubes are arranged next to one another and with the side faces whichinclude the long sides of their cross section parallel to one another,forming a flow path through which cooling air is routed. Cooling fins,which are responsible for effective heat exchange between the flat tubesand the cooling air stream, are arranged between the flat tubes in theflow path. After the cooling air stream has passed through, the flattubes open out into a second header passage, which feeds the cooled,compressed charge air flowing into it for combustion in the engine.

In heat exchangers, such as in particular charge-air coolers of thistype, the tubes are usually fitted into openings in a tube plate andsoldered in place in a fluid-tight manner. Each time that compressed airis applied, this soldered join or joints is subject to high mechanicalloads on account of rapid pressure changes. In particular the narrowsides of flat tubes do not satisfy the increasing demands on strength,which can result in leaks in particular in regions of tube-plate joinsor joints of this type which face the sides of the tube plate.

A simple way of increasing the strength of tube-plate joins is to usetubes and/or tube plates with a greater wall thickness or externaland/or internal fins with a greater material thickness. The increasedmechanical stability is useful in both cases, but the increased outlayon materials costs and weight required is very high.

Other proposed solutions deal with a reduction in the mechanical loadingon the tube-plate joins by the use of tie rods in the charge-air boxes.These tie rods stabilize the charge-air boxes and thereby relieve theload on the tube-plate joins, but also increase the outlay on materialand the pressure loss caused by the charge-air cooler.

The object of the invention is to provide a heat exchanger, inparticular a charge-air cooler, in which mechanical loads on tube-platejoins are reduced without an increased outlay on materials.

This object is achieved by a heat exchanger having the features of claim1.

According to claim 1, a heat exchanger has tubes which are suitable tohave a first medium flowing through them and a second medium flowingaround them, so that heat can be transferred from the first medium tothe second medium or vice versa. At least one header box which is incommunication with the tubes comprises at least one tube plate, whichhas a substantially planar central region and at least one side regionwhich is rounded or angled-off with respect to the central region. It ispreferable for the tube plate to have two in particular opposite sideregions which are rounded or angled-off with respect to the centralregion. In the central region there are tube openings, into which thetubes can be inserted in order to form the communicating connection tothe header box.

Working on the basis of the discovery that the geometry of the headerbox under compressive load approximates to a spherical form as a resultof deformation, since the shape of a sphere has the largest possiblevolume of all three-dimensional bodies for a given surface area, thebasic idea of the invention is to approximate the geometric shape of across section through the tube plate to a sector of a circle, so thatdeformations which occur as a result of a compressive load on the headerbox are reduced, thereby reducing the mechanical loads on connections oftubes to the tube plate. For this purpose, at least one of the tubeopenings in the central region of the tube plate advantageously extendsto the at least one side region or into the at least one side region.This ensures that at least one region of the tube-plate join, whichfaces the side region, adjoins a region of the tube plate which isrounded or angled off with respect to the central region. As a result,this region of the tube-plate join is located in a region of the headerbox which, in the case of compressive loads, has a reduced deformationand therefore reduced mechanical stresses. It is preferable for the tubeopening to extend into the rounded or angled-off side region, but evenif it only extends to the side region the mechanical loads on atube-plate join are already reduced.

The configuration of the heat exchanger according to the inventionincreases its mechanical strength and therefore also its service lifewithout requiring an increased outlay on materials, an increased numberof parts or a longer production time.

In the context of the present invention, a central region of a tubeplate is to be regarded as substantially planar if the tube plate ismostly planar in this region. In particular a tube plate central regionwith edges of tube openings which are deformed to produce what aredescribed as rims and/or with other minor deviations from planarity isto be considered as substantially planar in the context of theinvention.

Advantageous embodiments of the invention form the subject matter of thesubclaims.

According to one embodiment, the at least one side region of the tubeplate comprises one or more planar subregions, so that the header boxhas a faceted form. This allows reliable production with lowmanufacturing tolerances.

It is preferable for the at least one side region to have a roundedportion with an approximately constant radius of curvature or aplurality of rounded portions with different radii of curvature. Thisresults in a particularly good approximation to a semicircular crosssection of the tube plate.

A continuously convex form of the at least one side region also servesto improve the approximation to a semicircular shape of the tube platecross section. Concave subregions which are subject to high levels ofdeformation in the event of compressive loads are thereby avoided.

According to an advantageous configuration, the tube plate has rimswhich delimit the tube openings and as appropriate face into the headerbox or out of the header box. These rims serve to increase the contactsurface area between the inserted tubes and the tube plate, therebystrengthening the tube-plate join. It is particularly advantageous forthe rim of the at least one tube opening at or in the at least one sideregion to be lower than in the central region of the tube plate. Thisreduces the surface area on which mechanical stresses emanating from theside region can act on the tube-plate join, whereas a high stability ofthe tube-plate join is retained in the central region of the tube plate.

According to a preferred refinement, the heat exchanger according to theinvention is designed as a charge-air cooler which can particularlypreferably be used in motor vehicles. In particular, the charge-aircooler has two header boxes, a first of which is intended to distributecharge air and a second of which is intended to collect charge air. Itis advantageous for each of the header boxes to have precisely one tubeplate, which is provided with a row of tube openings. It is alsoadvantageous to use a row of flat tubes with in particular solderedcorrugated fins between them, since this increases the heat-transfersurface area. The cooling medium used is preferably air, although othercooling media, such as water or coolant, are also conceivable.

The invention is explained below on the basis of exemplary embodimentsand with reference to the drawings, in which:

FIG. 1 a: shows an excerpt from a heat exchanger according to thepresent invention,

FIG. 1 b: shows an excerpt from a heat exchanger,

FIG. 1 c: shows a cross section through a heat exchanger,

FIG. 2 a: shows an excerpt from a heat exchanger,

FIG. 2 b: shows an excerpt from a heat exchanger, and

FIG. 2 c: shows a cross section through a heat exchanger.

FIG. 1 a shows an excerpt from a heat exchanger 10 in the form of aperspective illustration. A header box 20 for distributing a firstmedium comprises a tube plate 30 and a box cover 40, which are welded toone another at a common contact surface 50. In this case, the box cover40 is fitted into the tube plate 30. However, it is also conceivable forthe box cover 40 to be fitted onto the tube plate 30 or attached to thetube plate 30 in some other way. In other exemplary embodiments (notshown), a tube plate and a box cover are joined to one another bysoldering, adhesive bonding or a positive lock or are formed as a singlepart or integrally with one another, i.e. for example from a deformedplate. The tube plate 30 has a tube opening 60, the edge 70 of which isdeformed into the interior of the header box as what is described as arim. A substantially rectangular flat tube 80 is fitted into the tubeopening 60 and soldered or welded to the tube plate 30. Corrugated finswhich adjoin the flat tube 80 on both sides and are soldered to the flattube, so that heat transfer from the first medium to a second mediumflowing around the tube 80 and the fins or from the second medium to thefirst medium is increased, are not shown. In total, the heat exchanger10 comprises an entire row of alternating flat tubes and corrugatedfins, which form what is known as a tube-fin block.

As can be seen from the side view shown in FIG. 1 b, the tube 80 isfitted into the tube opening 60 sufficiently far for an upper edgeregion 90 of the tube 80 to project beyond the rim 70. This ensures goodutilization of an inner surface, which cannot be seen but faces the tube80, of the rim 70 as a bearing surface for a tube-plate join. Thisserves, for example, to ensure sealed soldering. To avoid anunnecessarily high pressure drop of the first medium across the heatexchanger, the extent to which the tube 80 projects above the tube plate30 is to be minimized. For this reason, the tube opening 60 is locatedin a substantially planar central region 100 of the tube plate 30.

If the header box 20 is acted on by the first medium, the header box 20is under certain circumstances deformed in such a manner that itscross-sectional shape approximates to a circular shape. To, as it were,anticipate such deformation, side regions 110, 120 of the tube plate 30are angled off with respect to the central region 100. This results inreduced deformation of the tube plate 30 when the header box 20 is undercompressive load in these side regions 110, 120. The end sides 130, 140of the flat tube 80, which in mechanical terms are under the highestloads in the event of such pressure-induced deformations, are relievedof load by virtue of the fact that the tube opening 60 and thereforealso the tube 80 extend into the side regions 110, 120 of the tube plate30. The reduced deformation of the tube plate 30 which is present therereduces the mechanical load on the tube 80 and/or the tube-plate join.

FIG. 1 c shows a cross section through the heat exchanger excerpt fromFIG. 1 a or FIG. 1 b, the section plane running transversely through thetube 80. When this view is compared with FIG. 1 b, it can be seen thaton account of the fact that the tube opening 60 extends into the sideregions 110, 120 of the tube plate 30, which are angled off with respectto the central region 100, the rim 70 has a reduced height at the endsides 130, 140 of the flat tube 80. This brings the additional advantagethat there is a reduced surface area on the tube 80 for pressure-induceddeformations to act upon. The reduction in the bearing surface area forthe tube-plate join which is accepted at the same time can be tolerated,since a significantly larger part of the rim 70 retains a height whichis sufficient to stabilize the tube-plate join in the planar centralregion 100 of the tube plate 30.

FIGS. 2 a, 2 b and 2 c, analogously to FIGS. 1 a, 1 b and 1 c, show afurther exemplary embodiment of a heat exchanger 210 according to theinvention, which differs from the previous exemplary embodiment mainlyby virtue of the fact that the rim 270 is deformed such that it facesout of the header box 220. The tube plate 230 is welded to a box cover240 at the common contact surface 250. A substantially rectangular flattube 280 has been fitted into the tube opening 260 having the rim 270and soldered or welded to the tube plate 230.

To reduce a pressure drop across the heat exchanger in a first mediumflowing through the header box 220 and inter alia through the tube 280,the rim 270 faces out of the header box 220, so that the tube 280, whichhas been fitted in the rim 270, does not project above the tube plate230 in its substantially planar central region 300. Side regions 310,320 of the tube plate 230 are angled off with respect to the centralregion 300, in order to reduce deformation of the header box 220 undercompressive load at least in the side regions 310, 320. To relieve theload on the end sides 330, 340 of the flat tube 280, the tube opening260 and therefore the tube 280 extend as far as the side regions 310,320, as can be seen particularly clearly from FIG. 2 c.

Although in this exemplary embodiment the advantage of the reduced rimheight is no longer present, the load on the tube 280 and/or thetube-plate join is nevertheless likewise reduced on account of theS-shaped cross section of the tube plate 230 in the cover connection250—side region 310/320—rim 270 region.

1. A charge-air cooler having tubes and at least one header box to whichthe tubes are connected, the header box being configured to receive hotcompressed charge-air that is subject to rapid pressure changes andhaving at least one tube plate, the tube plate having (i) asubstantially planar central region with tube openings formed thereinand into which the tubes are fitted and secured with a sealed joint, and(ii) at least one side region which is rounded with a substantiallyconstant radius of curvature with respect to the central region, whereinthe at least one tube opening extends from within the generally planarcentral region at least up to the at least one side region and whereinthe at least one tube opening is delimited by a rim which extends out ofthe tube plate in a direction away from the at least one header box,whereby said rounded side portion of the tube plate and said rimadjacent to said rounded side portion form in cross-section a generallyS-shaped configuration sufficient to decrease load on said sealed jointas a result of said joint being subjected to rapid pressure changesexerted by the hot compressed charge-air.
 2. The heat exchanger asclaimed in claim 1, wherein the at least one side region has a pluralityof rounded portions with different radii of curvature.
 3. The charge-aircooler as claimed in claim 1, wherein the at least one side region isconvex in form viewed from the side of the tube plate facing away fromthe header box.
 4. A charge-air cooler having tubes and at least oneheader box to which the tubes are connected, the header box having atleast one tube plate and being configured to receive hot compressedcharge-air that is subject to rapid pressure changes, the tube platehaving (i) a planar central region with tube openings formed therein andinto which the tubes are fitted and secured with a sealed joint, and(ii) at least one side region which is rounded with a substantiallyconstant radius of curvature with respect to the central region, andmeans for decreasing load on said sealed joint as a result of said jointbeing subjected to rapid pressure changes exerted by the hot compressedcharge-air, said means comprising the at least one tube openingextending from within the generally planar central region at least up tothe at least one side region and the at least one tube opening beingdelimited by a rim which extends out of the tube plate.
 5. A charge-aircooler as claimed in claim 4, wherein the rim extends in a directiontoward the at least one header box and wherein the at least one tubeopening extends into the at least one side region by a distance largeenough to cause the rim in the at least one side region to extend out ofthe tube plate by a distance that is less than the distance the rimextends in the planar central region of the tube plate, whereby there isformed a reduced area for pressure-induced deformation of the tube plateto act on said sealed joint.
 6. A charge-air cooler as claimed in claim4, wherein the rim extends in a direction away from the at least oneheader box and wherein said rounded side portion of the tube plate andsaid rim adjacent to said rounded side portion form in cross-section agenerally S-shaped configuration sufficient to decrease load on saidsealed joint as a result of said joint being subjected to rapid pressurechanges exerted by the hot compressed charge-air.